Apparatus and method for controlling pressing force of separation roller

ABSTRACT

There is provided a method in which a conveyance force of a feed roller applied to recording paper is maintained constant in a period from the start to the end of use of the feed roller and a separation roller. The separation roller pressing force control method according to the present invention is such that a pressing force of the separation roller applied to the feed roller is set to be low in a variable range (Sa) such as the start of use in which the coefficient of friction of the feed roller is high, so that the conveyance force applied to the recording paper is not too large. As the coefficient of friction gradually decreases in accordance with the use of the feed roller, the pressing force of the separation roller is made to be gradually raised, thereby increasing the conveyance force applied to the recording paper and retaining it in a stable area Sb. As a result, reduction in the coefficient of friction and the conveyance force in accordance with the use of the feed roller and the separation roller is canceled or offset by adjusting the pressing force of the separation roller applied to the feed roller, whereby the feed roller can always feed the sheets of recording paper at a constant conveyance force, thus making it possible to prevent defective conveyance and defective separation of the sheets of recording paper.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus forcontrolling a pressing force of a separation roller, and moreparticularly, to a separation roller pressing force control apparatusand method for successively feeding sheets of recording paper one by oneby passing the sheets between a feed roller and a separation roller in acopying machine or the like.

[0003] 2. Description of the Related Art

[0004] A feed roller and a separation roller, generally used in acopying machine or the like, serve to feed (pass) sheets of recordingpaper one by one with the sheets being not superposed with each other,by clamping the recording paper sheets between both of the rollersthrough application of a constant pressing force. In general, EPDMs(ethylene propylene rubbers) and the like are used as materials for thefeed roller and the separation roller. However, these materials have acoefficient of friction which is high at the beginning of their use,decrease as the use proceeds, and then become stabilized and settled ina prescribed value. When the pressing force of the separation rolleragainst the feed roller is retained constant, a coefficient ofconveyance force with respect to the recording paper based on thecoefficient of friction of the feed roller (and the separation roller)provides a conveyance force (conveyance force coefficient×pressingforce) more than twice as much as a the pressing force at the beginning,as shown in FIG. 7, but at the time a paper feed of 4K (4,500) sheets orso is executed, the conveyance force produced decreases to about once(one-fold) of the pressing force.

[0005] In the known feed roller and the separation roller as describedabove, when the setting of the pressing force of the separation rollerwith respect to the feed roller is low, defective conveyance wouldresult due to slippage between the feed roller and the recording paper,whereas when the pressing force is high, defective sheet separation suchas two-sheet feed would take place. Thus, in order to solve thisproblem, there has been known a technique that a detection means, whichdetects the number of revolutions per minute of a separation roller, anda special motor are provided for making the conveyance force of the feedroller constant (for instance, Japanese patent application laid-open No.Hei 4-371426). However, there is a demand that defective conveyance anddefective separation are wanted to be prevented without usinglarge-scale (additional) members such as a sensor, a motor, etc., forthe purposes of reduction in cost and size.

SUMMARY OF THE INVENTION

[0006] The present invention is intended to solve the problems asreferred to above, and has for its object to provide a method andapparatus in which the conveyance force of a feed roller with respect torecording paper remains constant during a period from the start to theend of use of the feed roller and a separation roller without usinglarge-scale or additional members.

[0007] In order to solve the above-mentioned problem, the presentinvention resides in a separation roller pressing force controlapparatus for controlling a pressing force of a separation rollerapplied to a feed roller, the apparatus comprising: a separation rollerretention mechanism for retaining the separation roller in such a mannerthat the separation roller is pressed against the feed roller; and apressing force adjusting mechanism for maintaining a conveyance force ofthe feed roller applied to paper substantially constant by changing thepressing force of the separation roller in accordance with a change inthe coefficient of friction of the feed roller.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a graph illustrating the concept of a separation rollerpressing force control apparatus according to the present invention inan easy-to-understand manner.

[0009]FIG. 2 is a block diagram showing an embodiment of the separationroller pressing force control apparatus according to the presentinvention.

[0010]FIG. 3 is an enlarged view explaining the relation between a screwshaft and a movable arm shown in FIG. 2.

[0011]FIG. 4 is a view explaining the movements of respective componentparts at the time of replacement of a feed roller and a separationroller shown in FIG. 2.

[0012]FIG. 5 is a view explaining the movements of respective componentparts at the time of replacement of the feed roller and the separationroller shown in FIG. 2.

[0013]FIG. 6 is a block diagram showing another embodiment of aseparation roller pressing force control apparatus according to thepresent invention.

[0014]FIG. 7 is a graph illustrating a change in a conveyance force forrecording paper in a known feed roller.

DESCRIPTION OF THE PREFERRED ENBODIMENTS

[0015] Now, preferred embodiments of the present invention will bedescribed below based on the accompanying drawings. FIG. 1 is a graphillustrating the concept of a separation roller pressing force controlapparatus according to the present invention in an easy-to-understandmanner. FIG. 2 is a block diagram showing an embodiment of theseparation roller pressing force control apparatus according to thepresent invention. FIG. 3 is an enlarged view explaining the relationbetween a screw shaft and a movable arm shown in FIG. 2. FIGS. 4 and 5are views explaining the movements of respective component parts when afeed roller and a separation roller shown in FIG. 2 are replaced withnew ones. FIG. 6 is a block diagram showing another embodiment of aseparation roller pressing force apparatus according to the presentinvention. Here, note that the embodiments shown in FIG. 2 through FIG.6 are implementations of the contents of the invention to be describedlater and illustrated in FIG. 1 as apparatuses.

[0016] First of all, reference will be made to the adjustment of thepressing force of the separation roller applied to the feed rolleraccording to the present invention while using FIG. 1. As alreadyexplained with reference to FIG. 7, the coefficient of friction of thefeed roller gradually decreases in accordance with the number of sheetsof recording paper being fed in a variable range Sa at the start of useof the roller. Accordingly, the coefficient of conveyance force based onthe coefficient of friction also decreases gradually, and when thenumber of paper sheets fed becomes around 4.5 K, the coefficient ofconveyance force enters a stable area Sb and becomes substantiallyconstant. Therefore, in the variable range Sa, the pressing force of theseparation roller against the feed roller is gradually increased so thatthe reduction in the coefficient of conveyance force of the feed rollercan be canceled out or offset, whereas when the coefficient ofconveyance force has entered the stable area Sb, the pressing force ofthe separation roller is kept constant.

[0017] The separation roller pressing force control apparatus shown inFIG. 2 is used for feeding sheets of paper in a copying machine or thelike. In the case of this example, a drive motor 10 is mounted on amotor mounting frame 11. A feed roller 20 has a rotating shaft 21 withits one end supported by the motor mounting frame 11, and a rollerportion 22 attached to the other end of the rotating shaft 21. Thisrotating shaft 21 is supported by a support plate 24 with a bearing 23attached thereto at a location near the roller portion 22. In this case,the support plate 24 is fixedly secured to an upper frame (not shown).

[0018] A separation roller 30 has a rotating shaft 31 with its one endsupported by the motor mounting frame 11, a torque limiter 39 arrangedat the other end of the rotating shaft 31, and a roller portion 32attached to the torque limiter 39. This rotating shaft 31 is supportedby a support plate 34 with a bearing 33 attached thereto at a locationnear the roller portion 32. In this case, the support plate 34 isfixedly secured to a lower frame 90, but the bearing 33 is arranged inan elongated hole formed in the support plate 34 for vertical movement.A release lever 40 is arranged along the separation roller 30 on thelower frame 90 below the separation roller 30 in such a manner that itis rotatable about a support shaft 41 within a vertical plane. In thiscase, the support plate 34 is arranged so as not to obstruct therotation of the release lever 40.

[0019] A pressure arm 50 is rotatably mounted on a support shaft 51,which is fixedly secured to a cut-out and bent-up or upright portion 91formed on the lower frame 90, in such a manner that it is rotatable on avertical plane parallel to the plane of rotation on which the releaselever 40 is rotatable. A pressure spring 55 in the form of a coil orhelical spring has one end thereof attached to a lower end of thepressure arm 50 so that the pressure arm 50 is thereby pulled in adirection toward the motor mounting frame 11. The pressure arm 50 has anupper end in abutment with a lower end of the bearing 33 so as to applya pressing force corresponding to the tensile force of the pressurespring 55 to the bearing 33 and hence the separation roller 30, therebypushing it up toward the feed roller 20. A screw shaft 60 has one endthereof rotatably mounted on the motor mounting frame 11, and the otherend thereof rotatably mounted on a cut-out and bent-up or uprightportion 92 formed on the lower frame 90. A screw groove 61 with agradually changing screw pitch is formed on the surface of the screwshaft 60. The screw shaft 60 is driven to rotate in a directionindicated by an arrow RA at a location near the motor mounting frame 11by means of the drive motor 10, which drives the feed roller, etc.,through a speed reduction mechanism 80 using gears.

[0020] A movable arm 70 has one end thereof mounted on a support shaft94 fixedly secured to the lower frame 90, and in this case, the mountingof the movable arm 70 to the support shaft 94 is made such that an angleof the movable arm 70 relative to the support shaft 94 can be varied inthe vertical direction to some extent so as to permit the movable arm 70to freely rotate in the horizontal direction. A protrusion 71 (FIG. 3)is formed on a lower surface of the movable arm 70 at the other endthereof, and it is placed into fitting engagement with the screw groove61 of the screw shaft 60. This protrusion 71 extends to some extent inthe longitudinal direction of the movable arm 70. In addition, the otherend of the pressure spring 55 is attached to the movable arm 70 at alocation slightly closer to the support shaft 94 from the protrusion 71.In this case, the movable arm 70 operates between the rotating shaft 31and the release lever 40 when operating normally as shown in FIG. 2, butit is pushed toward the screw shaft 60 under the action of the resilientforce of the pressure spring 55.

[0021] Now, reference will be made to the successive operation of theseparation roller pressing force control apparatus of FIG. 2 whilereferring to FIG. 3. At the time when a new feed roller 20 and a newseparation roller 30 begin to be used, the movable arm 70 has beenturned to the side of the pressure arm 50, with the protrusion 71 beingin engagement with a start groove MS, as shown in FIG. 3. Accordingly,the protrusion 71 of the movable arm 70 is located at a position nearestto the pressure arm 50, so the force applied to the pressure arm 50through the pressure spring 55 is smallest and hence the pressing forceapplied to the separation roller 30 by the pressure arm 50 is least orminimum. On the other hand, the coefficients of friction of the new feedroller 20 and the new separation roller 30 (and the conveyance forcecoefficient or conveyance force based on the coefficients of frictionforce) are greatest, so the large coefficients of friction are offset bythe small pressing force, whereby the conveyance force becomes a desiredvalue.

[0022] As the feed roller 20 and the separation roller 30 are started tobe used, they serve to separate and convey sheets of recording paper oneby one. At this time, the screw shaft 60 is driven to rotate in thedirection of the arrow RA (FIG. 2) at a low speed through the speedreduction mechanism 80, so that the protrusion 71 of the movable arm 70is caused to move from the start groove MS to a variable pitch grooveMV. Thus, the protrusion 71 of the movable arm 70 is advanced in adirection indicated by an arrow DA (FIG. 3) to finally enter an endgroove MZ. The variable pitch groove Ml has a pitch which is coarse at alocation near the start groove MS, and which becomes finer and finer asthe distance thereof from the start groove MS increases. Therefore,while the protrusion 71 is moving within the variable pitch groove MV,the pressure spring 55 is stretched or expanded at a fast speed at first(i.e., in the variable range Sa of FIG. 1), and hence the force appliedto the pressure arm 50 through the pressure spring 55 is also increasedat a fast speed. The rate of stretching or expansion of the pressurespring 55 is gradually slowed down, so the force applied to the pressurearm 50 through the pressure spring 55 gradually increases at a slowerspeed, and finaly becomes constant.

[0023] As described above, by changing the pitch of the screw grooveformed in the screw shaft 60 in a manner as shown in FIG. 3, thepressing force of the roller portion 32 of the separation roller 30applied to the roller portion 22 of the feed roller 20 can be changed ina manner as shown in a characteristic curve of FIG. 1. Accordingly, theconveyance force applied to the recording paper by the roller portion 22of the feed roller 20 does not change in accordance with the number ofsheets of paper being fed (i.e., the number of sheets passed), thusmaking it possible to feed the sheets of recording paper with a constantforce. As the conveyance force applied to the recording paper remainsconstant, there will not be any defective conveyance and defectiveseparation of the recording paper. Moreover, since the apparatus isconstructed of mechanical component members of simple structure alone,it is simple in construction, low in cost and small in space, ascompared with the known one using a detection means for detecting thenumber of revolutions per minute of a separation roller as well as aspecial motor.

[0024] Next, reference will be made to the case in which in theseparation roller pressing force control apparatus of FIG. 2, the feedroller and the separation roller after having been fully used arereplaced with new ones, while referring to FIG. 4 and FIG. 5. When thefeed roller 20 and the separation roller 30 have been fully used, themountings (for instance, E rings) of the rotating shafts 21, 31 of thefeed roller 20 and the separation roller 30 to the motor mounting frame11 are removed (in this connection, note that the separation roller 30and the feed roller 20 are generally replaced with new ones at the sametime). At this time, the protrusion 71 of the movable arm 70 is usuallyin engagement with the end groove MZ of the screw shaft 60. First ofall, the feed roller 20 is pulled out in a direction indicated by anarrow DB, and then the separation roller 30 is pulled out in thedirection of the arrow DB. When the separation roller 30 is pulled out,the roller portion 32 abuts against a lamp 42 of the release lever 40,whereby the lamp 42 is depressed in a direction indicated by an arrowRB, as shown in FIG. 5.

[0025] When the roller portion 32 has depressed the lamp 42 of therelease lever 40, the release lever 40 is rotated about the supportshaft 41, thereby pushing up the movable arm 70. When the movable arm 70has been pushed up, the protrusion 71 of the movable arm 70 is releasedfrom the end groove MZ of the screw shaft 60, whereby the protrusion 71of the movable arm 70 is returned to the position of the start groove MSunder the action of the resilient force of the pressure spring 55, asshown by an arrow RC in FIG. 5. When the separation roller 30 is furtherpulled out so that the roller portion 32 has passed through the lamp 42,the protrusion 71 of the movable arm 70 is brought into engagement withthe start groove MS. When the separation roller 30 is freshly installed,the protrusion 71 of the movable arm 70 comes off from the start grooveMS, similar to the time when the separation roller 30 is pulled out, butit is again placed into engagement with the start groove MS.Accordingly, when the separation roller 30 (the feed roller 20) isreplaced with a new one, the initial setting of the pressing force ofthe new separation roller 30 is automatically carried out with a simplestructure. However, it is of course possible, if necessary, to set theposition of the protrusion 71 of the movable arm 70 to a desiredposition on the screw shaft by pressing the lamp 42 of the release lever40 with a finger, etc., to release the protrusion 71 of the movable arm70 from the screw groove, in the state shown in FIG. 2.

[0026] Now, reference will be made to another embodiment of a separationroller pressing force control apparatus according to the presentinvention while referring to FIG. 6. In the separation roller pressingforce control apparatus of FIG. 6, a rotating plate 160 with a spiralgroove is used instead of the screw shaft 60 of FIG. 2. The rotatingplate 160 is driven to rotate by means of a drive motor 110 through aspeed reduction mechanism 180. A protrusion (not shown) is provided on alower surface of a movable arm 170 at a free end thereof, and it is inengagement with a spiral groove 161 in the rotating plate 160. At thestart of use of a separation roller 130 (and a feed roller 120), theprotrusion on the movable arm 170 is in engagement with an outermostspiral groove 161 at a location near a pressure arm 150. The protrusionon the movable arm 170 is caused to gradually move to a center portionof the rotating plate 160 in accordance with the increasing number ofsheets of paper being fed. Thus, a pressure spring 155 is caused toexpand in accordance with the increasing number of sheets of paper beingfed, so the pressing force of the separation roller 130 applied to thefeed roller 120 is accordingly increased by means of the pressure arm150. In this connection, note that the function of a release lever 140is the same as that of the release lever 40 of FIG. 2.

[0027] As described above, in the variable range Sa shown in FIG. 1, thecoefficient of conveyance force based on the coefficient of friction ofthe feed roller gradually decreases in accordance with thecharacteristic curve in the variable range Sa shown in FIG. 1, that is,the coefficient of conveyance force with respect to the recording papergradually decreases in accordance with the characteristic curve. Theseparation roller pressing force control apparatuses shown in FIG. 2 andFIG. 6 increase the pressing force of the separation roller applied tothe feed roller in accordance with the decreasing conveyance force(conveyance force coefficient×pressing force) applied to the recordingpaper, whereby reduction in the coefficient of friction of the feedroller in the variable range Sa is canceled or offset to keep theconveyance force of the feed roller applied to the recording paper at aconstant value in a period from the start of use of the feed roller tothe end of use thereof. In addition, since such operation is achieved bysimple mechanical or structural members, the apparatuses are low incost, and advantageous for the reduction in size.

[0028] Since a method and apparatus for controlling the pressing forceof a separation roller according to the present invention areconstructed in a manner as described above, when the coefficient offriction of a feed roller is high, the conveyance force applied torecording paper can be controlled so as not to be too large by settingthe pressing force of the separation roller against the feed roller to asmall value, whereas when the coefficient of friction graduallydecreases in accordance with the use of the feed roller, the pressingforce of the separation roller against the feed roller is graduallyraised to increase the conveyance force applied to the recording paper.As a result, reduction in the coefficient of friction and the conveyanceforce in accordance with the use of the feed roller and the separationroller is canceled or offset by adjusting the pressing force of theseparation roller applied to the feed roller, whereby the feed rollercan always have a constant conveyance force. Thus, it is possible toprevent defective conveyance and defective separation with respect tothe recording paper. Moreover, such operation can be achieved by simplemechanical or structural members, and hence the apparatus is low in costand advantageous for the reduction in size. Furthermore, in adevelopment example, the initial setting of the pressing force of theseparation roller applied to the feed roller is automatically carriedout at the time when the feed roller and the separation roller arereplaced with new ones, thereby providing ease of use.

What is cliamed is:
 1. A separation roller pressing force controlapparatus for controlling a pressing force of a separation rollerapplied to a feed roller, said apparatus comprising: a separation rollerretention mechanism for retaining said separation roller in such amanner that said separation roller is pressed against said feed roller;and a pressing force adjusting mechanism for maintaining a conveyanceforce of said feed roller applied to paper substantially constant bychanging the pressing force of said separation roller in accordance witha change in the coefficient of friction of said feed roller.
 2. Theseparation roller pressing force control apparatus as set forth in claim1, wherein said pressing force adjusting mechanism changes the pressingforce of said separation roller applied to said feed roller by using adriving force of said feed roller.
 3. The separation roller pressingforce control apparatus as set forth in claim 2, wherein said pressingforce adjusting mechanism comprises: a pressure arm having its one endheld for rotation about a pressure arm support shaft so as to press saidseparation roller toward said feed roller; a pressure spring having itsone end attached to the other end of said pressure arm; a movable armhaving one end thereof held for rotation about a movable arm supportshaft and the other end thereof to which is attached the other end ofsaid pressure spring; a speed reduction mechanism for performingtransmission of the driving force of said feed roller; and a pressurespring expansion mechanism adapted to receive the driving forcetransmitted from said speed reduction mechanism to set a tensile forceof said pressure spring to a low value at the start of use of said feedroller, and to increase the tensile force of said pressure springapplied to said pressure arm in accordance with the increasing number ofsheets of paper being fed thereby to gradually increase the pressingforce applied to said separation roller by said pressure arm.
 4. Theseparation roller pressing force control apparatus as set forth in claim3, wherein when the number of sheets of paper being fed has reached athreshold, said pressure spring expansion mechanism maintains thepressing force which is applied to said separation roller by saidpressure arm at that time.
 5. The separation roller pressing forcecontrol apparatus as set forth in claim 3, wherein said pressure springexpansion mechanism comprises a screw shaft which is arranged to extendin a direction toward said pressure arm, and which is driven to rotateunder the action of the driving force from the speed reductionmechanism, and a screw groove of an irregular pitch is formed on theouter periphery of said screw shaft, so that the one end of said movablearm is engageable with said screw groove.
 6. The separation rollerpressing force control apparatus as set forth in claim 5, wherein saidscrew shaft has a start groove formed on the outer periphery thereof atan end portion thereof near said pressure arm, an end groove formed onthe outer periphery thereof at an end portion thereof away from saidpressure arm, and a screw groove formed on the outer periphery thereofbetween said start groove and said end groove, said screw groovestarting from said start groove with a coarse pitch, and being connectedwith said end groove with its pitch becoming gradually finer and finer.7. The separation roller pressing force control apparatus as set forthin claim 3, wherein said pressure spring expansion mechanism comprises arotating plate which is formed on its surface with a spiral grooveextending from its center of rotation, and which is caused to rotate bythe driving force from said speed reduction mechanism, and a screwgroove of an irregular pitch is formed on the surface of said rotatingplate, with the other end of said movable arm being engageable with saidscrew groove.
 8. The separation roller pressing force control apparatusas set forth in claim 7, wherein said rotating plate is formed on itssurface with a spiral groove extending from its center of rotation andis caused to rotate by the driving force from said speed reductionmechanism, and said rotating plate has a start groove formed on itsoutermost periphery, and an end groove formed at its center of rotation,and a screw groove of an irregular pitch formed on its outer peripherybetween said start groove and said end groove, said screw groovestarting from said start groove with a coarse pitch, and being connectedwith said end groove with its pitch gradually becoming finer and finer.9. A separation roller pressing force control method in which sheets ofrecording paper are passed between a feed roller and a separation rollerwith a pressing force of said separation roller applied to said feedroller being controlled so as to feed the sheets of recording paper oneby one, said method comprising: retaining said separation roller so asto permit said separation roller to move toward said feed roller; andmaintaining the pressing force of said separation roller applied to saidfeed roller at a constant value by changing the pressing force of saidseparation roller applied to said feed roller by the use of a drivingforce of said feed roller so as to offset a change in the coefficient offriction of said feed roller which changes in accordance with the numberof sheets of paper being fed.